1) To evaluate the lactating rodent as a test system for assessing the potential of xenobiotics to concentrate in human milk. 2) To investigate the ability of xenobiotics to qualitatively alter the composition of milk. Rationale and background: It is well-known that neonates can be exposed to drugs/chemicals (and their metabolites) indirectly by transfer of the compounds through milk. A variety of medicinals have been evaluated for their propensity to travel in human milk and physico-chemical relationships have been established which allow predictions for other chemicals. However, humans are exposed to a large number of industrial, environmental, and agricultural chemicals for which no milk data are available. Therefore, a focus of this project has been to evaluate the lactating rodent as a model for testing the potential lactational transport of chemicals for which human studies are unfeasible. Additionally, the effects of chemicals on the lactation process is a neglected area of study which may have important implications in the development of neonates. Consequently we are investigating the ability of toxicants to alter milk quality and milk quantity.